Industrial wastewater and the like can contain persistent substances that cannot be removed by existing ozone treatments. In particular, removal of dioxins, dioxane, and the like is a major problem. In some areas, a method of removing persistent substances by combining ozone (O3) with hydrogen peroxide (H2O2) or ultraviolet light, thereby causing hydroxyl radicals (OH radicals), which are higher in activity than ozone, to be generated in water to be treated, is in practical use.
However, as equipment and operation costs are very high, this method is not actually very prevalent. In view of this, a method has been proposed in which persistent substances are removed with high efficiency by causing OH radicals and the like generated by a discharge to act directly on water to be treated.
Specifically, such a conventional water treatment apparatus is provided with a layer-structured treatment means respectively including a reaction vessel capable of storing water to be treated in an interior thereof and pin-shaped electrodes that generate a discharge in order to perform discharge radical treatment on the water to be treated, and a power supply means for applying a high voltage to the electrodes. With such a radical treatment system, it is possible to improve efficiency in decomposing persistent substances dissolved in water using radicals (see PTL 1, for example).
Further, a water treatment apparatus has also been proposed in which water to be treated is treated by arranging, in an inclined state, a pair of electrode plates that vertically oppose each other so that water to be treated flows downward onto a lower electrode, and forming a barrier discharge between the electrodes. With such a water treatment apparatus, the water to be treated can be treated efficiently using a simple configuration (see PTL 2, for example).